Personally, I have no idea why. I know that if the post was something extremely generic from an "anonymous poster", like "Please help me learn English", one of the moderators would delete it immediately, but that's not your case. If it was a duplicate post or if it contained curse words or if it contained advertising, it would also have been deleted.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.